The present invention is concerned with a new cellulose moulded body and a process for the production of this cellulose moulded body. Particularly, the present invention is concerned with a new cellulose fibre and a new cellulose film having a predetermined tendency to fibrillation.
For the purposes of the present specification and claims, the term "moulded body" means particularly fibres and films. In the following, the term "fibres" means fibres, films and also other moulded bodies.
As an alternative to the viscose process, in recent years there has been described a number of processes wherein cellulose, without forming a derivative, is dissolved in an organic solvent, a combination of an organic solvent and an inorganic salt, or in aqueous saline solutions. Cellulose fibres made from such solutions have received by BISFA (The International Bureau for the Standardisation of man made Fibres) the generic name Lyocell. As Lyocell, BISFA defines a cellulose fibre obtained by a spinning process from an organic solvent. By "organic solvent", BISFA understands a mixture of an organic chemical and water.
The present invention is concerned with a specific process for the production of a cellulose fibre of the Lyocell type, wherein a cellulose solution is extruded across an air gap into an aqueous precipitation bath. In the following, this process will be referred to as amine-oxide process, wherein a tertiary amine-oxide, particularly N-methylmorpholine-N-oxide (NMMO), is used as a solvent. Such a process is described for instance in U.S. Pat. No. 4,246,221 and provides fibres which exhibit a high tensile strength, a high wet-modulus and a high loop strength.
A typical feature of the Lyocell fibres is their pronounced tendency to fibrillate when wet. Fibrillation means the breaking off of the fibre in longitudinal direction at mechanical stress in a wet condition, so that the fibre gets hairy, furry. The reason for fibrillation may be that the fibres consist of fibrils which are arranged in the longitudinal direction of the fibre axis and that there is only little crosslinking between these.
WO 92/14871 describes a process for the production of a fibre having a reduced tendency to fibrillation. The reduced tendency to fibrillation is achieved by providing all the baths with which the fibre is contacted before the first drying with a maximum pH value of 8,5.
WO 92/07124 also describes a process for the production of a fibre having a reduced tendency to fibrillation wherein the freshly spun, i.e. never dried fibre is treated with a polymer that can be made cationic. As such a polymer, a polymer having imidazole and azetidine groups is mentioned. Additionally, there may be carried out a treatment with an emulsifiable polymer, such as polyethylene or polyvinylacetate, or a crosslinking with glyoxal.
In a lecture given by S. Mortimer at the CELLUCON conference in 1993 in Lund, Sweden, it was mentioned that the tendency to fibrillation rises as drawing is increased.
There have been published already some methods to reduce the tendency to fibrillation of Lyocell fibres:
Thus from WO 95/02082 of the applicant it is known that fibrillation may be reduced by certain combinations of spinning parameters.
Moreover, it is known that the fibrillation properties of Lyocell fibres may be improved by chemical crosslinking. Thus, e.g. EP-A-0 538 977 describes crosslinking of Lyocell fibres with chemical reagents able to react with cellulose in the never dried state, i.e. when the fibre is produced, as well as in the dried state, i.e. substantially during the textile finishing of the plane fibre assemblies.
It is known further that the tendency to fibrillation of Lyocell fibres may be reduced by crosslinking them with glyoxal (M. Dube and R. H. Blackwell, TAPPI Proceedings; International Dissolving and Specialty Pulps, pages 111-119; 1983).
Crosslinking Lyocell fibres during their textile finishing has the main drawback for the finishing operator of requiring additional steps which cause additional costs. Also, the application of such additional steps limits the variety of produceable plane fibre assemblies, which again restricts the marketing possibilities of the Lyocell fibres. A further essential disadvantage of the treatment of Lyocell fibres after a first drying consists in that the susceptibility of the fibres for crosslinking chemicals is significantly reduced, particularly after the first drying, as compared to the state they exhibit when they are freshly spun. This requires the use of greater amounts of chemicals.
The crosslinking reagents exemplified in the patent application mentioned above exhibit as groups capable of crosslinking halogen-substituted, nitrogen-containing ring structures able to react with the hydroxyl groups of the cellulose in alkaline conditions. Moreover, compounds comprising vinyl sulphone groups or their precursors are described. These compounds substantially also react only when alkali is added, or they require alkali as a neutralisation reagent for cleaved acids. The procedures proposed in this patent application for crosslinking never dried Lyocell fibres have serious drawbacks insofar as it is difficult and requires a complex arrangement to carry them out in a continuous fibre post-treatment process. When very reactive compounds of the compound classes indicated are used, a separate application of the crosslinking substances from the basic compounds necessary to initiate the reaction with the cellulose is required. When less reactive compounds are used, frequently a simultaneous application of the crosslinking agents and the alkali is possible, but in this case a temperature step has to be carried out which in the indicated patent application is achieved by "steaming". Thus, a serious drawback of the indicated patent is an increase of the number of post-treatment steps, which implies a significant cost raise, especially when constructing a plant for the production of such a fibre.
However, there is still a further drawback to this procedure. When halogenated, nitrogen-containing rings or the vinyl sulphons and their precursor substances respectively are reacted, salts are formed during the crosslinking reaction which have to be washed out of the fibre afterwards. Moreover, also excess residual chemicals not reacted with the cellulose have to be washed out. This means that in a continuous fibre production process, a further post-treatment step is necessary, causing further investment and operating costs and creating additional problems with contaminated waste water.
In WO 94/24343 of the applicant, similar processes for crosslinking Lyocell fibres to reduce fibrillation describing the use of alkaline buffers and an exposure to electromagnetical waves as particularly advantageous are proposed.
WO 94/20656 describes a reduction of the fibrillation of Lyocell fibres by means of crosslinking using conventional crosslinking chemicals usually employed to improve crease angles of cellulose textiles while a simultaneous reduction of the dye absorption is prevented when the crosslinking is carried out in the simultaneous presence of flexible, linear polymers. Substantially, conventional N-methylol resins (containing a low formaldehyde level) and the usual acidic catalysts are used. This method is described as efficient for use on the dried as well as the never dried fibre.
However, also this procedure has drawbacks which make another crosslinking method desirable. The methylol resins usually employed for improving the wet crease angles need relatively high reaction temperatures, generally from 120.degree. C. to 160.degree. C., to react with the OH groups of the cellulose, when the reaction is to be carried out at a sufficient rate. In the international patent application indicated, also very high temperatures for fixing the crosslinking agents are applied. This always implies a more or less significant loss of fibre strength, but above all a loss of fibre elongation and loop strength, and the fibre is getting brittle. Moreover, in the cited patent application no comparative physical fibre data before and after the crosslinking reaction are indicated. Reactions with the cited N-methylol compounds at low temperatures und thus a higher fibre moisture, which do not imply such serious strength and elongation losses, usually require very long reaction times and therefore are hardly suitable for continuos fibre production processes.
In "Textile Research Journal", February 1969, pages 173-180, S. P. Rowland and M. A. F. Brannan describe that quaternized 2-(diethylamino)ethylcellulose produced from cotton fabric is capable of being crosslinked in the form of the hydroxy base with disulphone or bis-(2-hydroxyethyl)sulphone at room temperature in wet state or dry at a temperature of 140.degree. C., and that very good wet crease angles will result from wet crosslinking.
Moreover it is known that cellulose fibre textiles may be dyed with conventional reactive dyes at neutral pH values and without adding salt when they are appropriately pre-treated (Lewis et al., JSDC volume 107, March 1991, and JSDC volume 109, November 1993). The nitrogen hetero rings containing vinyl sulphone or halogens which under alkaline conditions usually react as anchoring groups with the hydroxy groups of the cellulose will react with the amino groups without addition of alkali, since they represent significantly stronger nucleophiles than the hydroxy groups.
In "Chemical Aftertreatment of Textiles" (H. Mark, N. S. Wooding, S. M. Atlas), page 414, a wet crosslinking of quaternized diethylaminocellulose in hydroxy form at room temperature is described.
From WO 95/15342 it is known to react cellulose with a carboxy methylating agent. EP-A-0 665 311 describes the production of aminated cellulose fibres by adding e.g. an amine-substituted cellulose derivative to a cellulose solution and spinning fibres from the solution.
In the Italian patent application 690,926 (1965), the inner salt of trissulfatoethylsulphonium is described for the alkaline crosslinking of gelatine. The reaction is carried out at pH 7 and at a temperature of 50.degree. C.